Recently, many studies regarding technological developments and projects related to bio-ethanol fuel have been published. However, the biggest problem with using bio-ethanol as a blending agent of fuel oil is that, upon introduction of water to ethanol-mixed gasoline, a water-ethanol mixture layer is separated from gasoline while water is absorbed into the mixed gasoline.
Gasoline mixed with butanol, methyl ester or ethyl butyrate, unlike such ethanol, does not absorb water even when water is introduced thereto, and thus layer separation thereof does not occur. Thus, gasoline mixed with butanol, methyl butyrate or ethyl butyrate does not need additional treatment in storage, transport infrastructure and vehicles, unlike ethanol-mixed gasoline.
The additional advantages of butanol, methyl butyrate and ethyl butyrate are that a heat value is higher and vapor pressure is lower than ethanol, thus decreasing a probability of generating vapor lock in engines for vehicles. In particular, because butanol has an air-to-fuel ratio close to that of gasoline, compared to ethanol, it may be added in a comparatively larger amount to gasoline in the range that does not affect performance of engines.
As shown in Table 1 below, however, butanol has an octane number approximately equal to that of gasoline, making it difficult to use as an octane booster such as ethanol, MTBE, or ETBE.
Methyl butyrate and ethyl butyrate are superior octane boosters to MTBE, and are not harmful to the human body to the extent of being useful as a fruity flavor, and are thus regarded as a material harmless to the environment and the human body when added to gasoline.
TABLE 1MethylEthylGasolineEthanolButanolbutyratebutyrateSolubility in waterInsolubleMiscible9.1 cc/100 cc15 g/L4.9 g/LMolecular weight & molecular—4674102116formulaC4-C12C2H5OHC4H5OHC5H10O2C5H12O2Density @20° C., g/cm20.720.790.810.8980.879Boiling point, ° C.32-21078117102121Flash point, ° C.−2012351226Heat value, Kcal/kg7,7005,0766,4046,0946,443Evaporation heat, Kcal/kg86200142——Air/fuel ratio14.69.011.2——Blending octane number (RON)91~99 12996125123Vapor pressure @ 100 F., kPa—14.91.2324.41.5(106-168)(23-30)
Despite the above advantages, the main reason why butyric acid derivatives such as methyl butyrate and ethyl butyrate are not used as fuel is that efficient production of butyric acid has not yet been achieved.
As mentioned above, methyl butyrate and ethyl butyrate may be used as octane boosters for gasoline blending, and ethyl butyrate may also be utilized as a solvent.
Moreover, as shown in Table 2 below, butyl butyrate has a cetane number of about 30, and a flash point which satisfies the standard of diesel, and thus may be utilized as novel bio-diesel. When butyl butyrate is hydrogenolyzed, only butanol is produced without generation of other ester byproducts, and thus, among ester compounds, butyl butyrate may be optimal for producing butanol.
TABLE 2Soybean bio-DieselEthyl butyrateButyl butyratedieselSolubility in waterInsoluble4.9 g/LInsolubleInsolubleMolecular weight & molecular—116144RCOOCH3formulaC5H12O2C3H7COOC4H5Density @20° C., g/cm20.820.8790.86920.87-0.89Boiling point, ° C.150~380121165340-380Flash point, ° C.40 or more2649180-185Heat value, Kcal/kg9,10064436,3508,300Blending cetane number500-1325-3040-45
In the case of a butyrate present in the form of a salt in a fermented liquid, that is, a broth, resulting from microorganism strains, even when alkylamine, which is a basic organic solvent having good extraction efficiency, is used as an extraction solvent, it is very difficult to extract butyric acid.
Conventional methods are disclosed in such a manner that an inorganic acid such as sulfuric acid is added to a broth so that a butyrate salt is converted into butyric acid, after which butyric acid is extracted with an extraction solvent. However, as a spent broth obtained after extraction contains ammonium sulfate or calcium sulfate, it is impossible to recover ammonia and calcium hydroxide from the broth, undesirably increasing the production cost.
On the other hand, butyric acid is esterified with the addition of butanol, and then hydrogenolyzed using a catalytic reactor, thus preparing butanol, which is disclosed in Korean Unexamined Patent Application Publication No. 2009-0103720.
However, processes of preparing low-molecular-weight alkyl ester useful as fuel oil from bio-derived butyric acid, in particular, microorganism-derived butyric acid, have not yet been known.